Plastic injection molding machines are well known, and they generally follow a standard sequence of operations. The operation of some of these prior art injection molding machines is described below with reference to certain U.S. patents; the entire disclosure of each of these patents is hereby incorporated by reference into this specification.
As is disclosed in U.S. Pat. No. 4,208,176, in many of the prior art injection molding machines, ". . . raw plastic material is fed into a cylinder . . . it heats and plasticizes the material and forces it to the front end of the barrel. . . . When a sufficient amount of material has accumulated to produce the desired molded article and after the mold parts have been clamped together, the . . . screw is then forced forward, injecting plastic melt into the mold cavity. . . . When the part has sufficiently solidified to maintain its shape without external pressure, the holding pressure is reduced. . . . The part is then either cooled or cured in the mold, depending upon whether the plastic is thermoplastic or thermosetting. When the plastic has sufficiently solidified and the part is sufficiently formed to be ejected from the cavity, the clamp is opened and the part is then ejected."
Many injection molds for use in such prior art machines are known to those skilled in the art. These are "closed molds," that is, in their use they are closed without any material in the mold. After the application of pressure to close the mold and to hold it tightly clamped against injection pressure, molten plastic material is forced into the closed mold cavity by a source of pressure other than that which caused the mold to close.
Illustrative of some of the injection molds which have been designed for use with injection molding machines are those molds described in U.S. Pat. Nos. 3,865,529 of Guzno and 3,905,740 of Lovejoy. The Guzno patent discloses a collapsible core structure for the injection molding of plastic articles which has particular utility in the molding of polygonal enclosures having an inwardly turned flange adjacent a top opening of the article. The Lovejoy patent discloses an injection mold for the manufacture of a plastic article having four side walls and only one closed wall forming a generally rectangular enclosure with an open top.
In many of the prior art injection molding machines, the direction of mold clamping and the direction of injection are the same. However, several patents have disclosed a horizontal mold clamping and vertical injection die casting machine See, for example, U.S. Pat. No. 4,655,274 of Dannoura.
The operation of some of the prior art injection molding machines is often dependent upon some physical property of the article being molded. Thus, by way of illustration, U.S. Pat. No. 4,208,176 discloses a plastic injection molding machine comprised of means for opening its mold clamp to eject the molded part in response to parameters based upon the actual physical properties of the plastic in the mold (such as temperature, or pressure).
The molded parts produced by the injection molding machines are usually ejected from the machines and often fed to a guide skirt, which collects such parts as they are ejected and thereafter releases them. See, for example, U.S. Pat. Nos. 4,295,815 and 4,741,687.
To the best of applicants' knowledge, the prior art has not provided an injection molding machine which is compact, which is relatively inexpensive to use, which is adapted to produce small molded plastic parts, which is substantially automatic, and which is comprised of adjustable means for accurately sensing the ejection of small molded parts.
It is an object of this invention to provide an injection molding machine which is relatively compact and inexpensive.
It is another object of this invention to provide an injection molding machine in which the direction of mold clamping and the direction of injection are different.
It is yet another object of this invention to provide an injection molding machine which can utilize a flat mold plate which can readily be made out of brass bar stock.
It is yet another object of this invention to provide an injection molding machine which can utilize a flat mold plate which can readily be inserted into or removed from the machine.
It is yet another object of this invention to provide an injection molding machine comprised of a standard flat mold plate with alignment and ejector pins in it.
It is yet another object of this invention to provide an injection molding machine which is adapted to automatically sense the ejection of the injection molded part from the machine.
It is yet another object of this invention to provide an injection molding machine which is capable of operating substantially automatically and requires minimal operator attention.